Converting hex to string in C?

Question

Hello I am using digi dynamic c. I am trying to convert this in to string

char readingreg[4];
readingreg[0] = 4a;
readingreg[1] = aa;
readingreg[2] = aa;
readingreg[3] = a0;

Currently when I do printf statements it has to be like this:

printf("This is element 0: %x\n", readingreg[0]);

But I want this in string so I can use printf statement like this

  printf("This is element 0: %s\n", readingreg[0]);

I am essentialy sending the readingreg array over TCP/IP Port, for which I need to have it as string. I cant seem to be able to convert it into string. Thanks for your help. Also if someone can tell me how to do each element at a time rather than whole array, that would be fine to since there will only be 4 elements.

Answer 1

0xaa overflows when plain char is signed, use unsigned char:

#include <stdio.h>

int main(void)
{
    unsigned char readingreg[4];
    readingreg[0] = 0x4a;
    readingreg[1] = 0xaa;
    readingreg[2] = 0xaa;
    readingreg[3] = 0xa0;
    char temp[4];

    sprintf(temp, "%x", readingreg[0]);
    printf("This is element 0: %s\n", temp);
    return 0;
}

Answer 2

If your machine is big endian, you can do the following:

char str[9];

sprintf(str, "%x", *(uint32_t *)readingreg);

If your machine is little endian you'll have to swap the byte order:

char str[9];
uint32_t host;

host = htonl(*(uint32_t *)readingreg);
sprintf(str, "%x", host);

If portability is a concern, you should use method two regardless of your endianness.

I get the following output:

printf("0x%s\n", str);

0x4aaaaaa0